(CBS) One of the unanswered questions of
September 11th is whether there was anything U.S. intelligence could have
done to stop the attacks. New information suggests a key to the conspiracy
could have been discovered before the attack - if it hadn’t been for what
appears to be a communication breakdown between the FBI and French
intelligence.

A month before September 11th, the FBI hauled in a
French citizen, Zacarias Moussaoui. He’s now in jail-- the only person
charged in the attacks. Prosecutors call him “the 20th hijacker.”

We now know that, back in August, Moussaoui’s possessions
contained evidence that would expose key elements of the September 11th
conspiracy. The FBI didn’t search Moussaoui’s things because it says it
didn’t have enough evidence for a search warrant. Critical evidence was in
the hands of French intelligence. The FBI says that if that evidence
exists, the Bureau never received it.

If there was a golden
opportunity to stop the attacks, Moussaoui was it. Prosecutors say he was
following the same path as the other 19 hijackers. But there was a
difference; Moussaoui couldn’t keep his mouth shut. That got him in
trouble in August when he was taking flight simulator training at a school
in Minnesota. He was a strange student with strange questions. He was
interested in flight patterns around New York City. He asked whether the
doors of a 747 could be opened in flight. And there was more.

He
paid for his flight lessons, nearly $7,000, in cash and he told his
instructors that he urgently needed to learn how to fly big jets, even
though at the time he didn't have so much as the license to fly a Cessna.
Within two days some of the instructors were openly talking about whether
Moussaoui might be a hijacking suspect, so they decided to call the FBI.

That was August 15th and the next day, FBI and immigration agents
staked out Moussaoui’s hotel. Sources familiar with the investigation
tells us when Moussaoui stepped out, the agents asked him about his flight
training and how he was paying for it.

Moussaoui told them that he
always wanted to learn how to fly and he was a successful salesman. The
FBI asked him what company he worked for and Moussaoui told the agents
that he couldn't remember. It was all downhill from there. Moussaoui
became belligerent - he told the agents that they wouldn't be harassing
him if he wasn't an Arab. The agents asked to see his personal belongings
and Moussaoui said no. The FBI didn't have any reason to arrest him at
that point, but Moussaoui had overstayed the 90 days that he was supposed
to be in the United States, so the immigration officer took him in.

They took him to the Sherburne County jail in Minnesota. The FBI
was sure Moussaoui was up to something. They actually discussed whether he
was plotting to crash a plane into a building in New York City. It was a
hunch and a brilliant one. They wanted to search Moussaoui’s laptop and
belongings. But they couldn’t without a warrant. So the agents asked FBI
headquarters in Washington to try to get a special search warrant under a
law called the Foreign Intelligence Surveillance Act — or FISA for short.

Until last year Eric Holder was deputy attorney general in the
Justice Department. One of his responsibilities was reviewing hundreds of
FISA applications. “Under FISA you have the ability, over a specified
period of time, to not only do one search, but to do a number of searches,
and then to take that from that person anything that's of foreign
intelligence value,” he says.

To get the search warrant, the FBI
needed evidence to link Moussaoui to a specific terrorist group. A
computer search at the National Security Agency and at the FBI, and CIA
found nothing. Moussaoui is a French citizen of Moroccan descent, so the
FBI asked French intelligence what they had.

The French had reason
to link Moussaoui to Osama bin Laden’s organization. 60
Minutes talked with several sources in French intelligence and
they all agree on three points. First, back as early as 1995 French agents
traced Moussaoui to Afghanistan on what they believe was a trip to an Al
Qaeda camp. Second, in 1999, the French put Moussaoui on a watch list of
potential terror suspects. Third, in 2000, French intelligence followed
Moussaoui to Pakistan. They believe he went to see a man named Abu Jaffa—a
top lieutenant to Osama bin Laden.

Jean-Louis Bruguiere is a
French judge and one of the world’s top terror investigators. The law
prevents him from talking about classified intelligence related to
Moussaoui, but he did tell 60 Minutes that French agents
were closely watching French citizens in Afghanistan.

“We know
that people were training in Afghanistan to come back in Europe and be
able to set up, organize and run terrorist networks,” he says.

Was
Moussaoui placed on a watch list of terrorist suspects in 1999? “If by a
watch list you mean everyone who could be of interest to the security
services, well then probably Mr. Moussaoui is on that list,” Bruguiere
says.

Bruguiere is famous for being a step ahead of most other
terror investigators—including one case similar to the Moussaoui
investigation. In 1999 Bruguiere wanted to question Al Qaeda’s Ahmed
Ressam, who was living in Canada. The Canadians refused and Ressam was
next seen in Washington state with a trunk load of explosives meant to
bomb the Los Angeles airport. Ressam was convicted last year. Bruguiere
says that when the FBI asked about Moussaoui, French intelligence was
eager to help.

“For this particular case, I can’t discuss the
specific details. But overall all the information we had, we handed it
over,” he says.

“We gave them everything we had,” says Bruguiere.
“Or what we knew when these requests were made.”

The French had
been following Moussaoui for years. In the 1990’s they tracked him to
London where he learned militant Islam from radical clerics including Abu
Qatada. French intelligence has linked Qatada to Osama bin Laden. Qatada
preaches a particularly violent brand of Islam and encourages Muslims to
take up jihad wherever they can. So Moussaoui took that advice and went to
Chechnya to join Muslims in their fight against Russian troops. French
intelligence was aware of that move and his later trip to Afghanistan.

The French had a thick file on Moussaoui. But U.S. government
sources tell us the FBI never received all the information from the
French. These sources say the French sent only a few pages to FBI
headquarters that described Moussaoui as an Islamic extremist and
dangerous—but never mentioned what the French believed about the bin Laden
connections in Afghanistan and Pakistan.

Three months after the
attacks, FBI director Robert Mueller said this about the effort to get the
search warrant. “All I can tell you is that the agents on the scene
attempted to follow up aggressively. The attorneys back at FBI determined
that there was insufficient probable cause for a FISA, which appears to be
an accurate decision. And September 11th happened.”

The FBI has
characterized the quality of French information after the arrest of
Moussaoui in August, as vague and sketchy - in other words, not very good.

“We don’t only give general information,” says Bruguiere. “We have
detailed information, we give as much detail as we know. If the FBI thinks
that the information is valuable, that’s its own responsibility.”

Judge Bruguiere refuses to criticize the FBI but he is adamant
that in the weeks before September 11th, French intelligence shared its
wealth of information on Moussaoui.

“French authorities have
always given all their partners, including the United States, all
information they had and I am sure that in this case, as in others, we
didn’t hide any information,” he says.

It’s not possible to
reconcile what the French say they sent and what the FBI says it received;
neither the French nor the FBI will let 60 Minutes see those
communications, and the FBI has declined an interview. We do know that by
the end of August, after a series of meetings at headquarters, FBI lawyers
decided they would not even try to get a warrant to search Moussaoui’s
things.

At the Minnesota jail, the FBI’s field agents felt their
backs were against a wall—headquarters told them they couldn’t search
Moussaoui’s possessions and time was running out before he would be
deported—so they tried something desperate.

They decided to try to
bluff Moussaoui into a confession. Federal sources familiar with this
investigation tell us that FBI agents came here for a final confrontation.
They told Moussaoui that they knew he was a terrorist, knew he was a
hijacker and they weren’t going to let him leave the country. The FBI
agents warned Moussaoui that he was in serious trouble, but he could still
help himself if would just told the FBI everything he knew.

But if
Moussaoui couldn’t keep his mouth shut before—he was certainly doing it
now. He did say if the agents just would let him go, he’d finish his
flight training and head back to France. His deportation was scheduled for
September 17th. The FBI planned to put him on a commercial flight with
three armed agents. In Paris, Moussaoui and his still untouched
possessions would be turned over to Judge Bruguiere. But, of course, that
never happened.

After September 11th the FBI got a search warrant
that its field agents had wanted for three weeks, and they immediately
found the evidence that led to key conspirators in the attacks. According
to Moussaoui’s indictment, the FBI found his notebook, listing a German
phone number. That number traced back to Ramzi bin al Shibh. Bin al Shibh
was the roommate of Mohammad Atta, the leader of the attacks. Bin al Shibh
and Atta created a German Al Qaeda cell together. Bin al Shibh wired tens
of thousands of dollars to Moussaoui and another hijacker, Marwan
al-Shehhi, who flew into the World Trade Center’s South tower.

“It's a good lead,” says Holder. “We certainly know more about
al-Shibh now than we did then. I don't know exactly what we knew about
him, you know, prior to September 11th, but clearly the connection to him,
the German connection, knowing now what we know about Atta and his German
connections, all of these things would have been important.

Of
course, that’s hindsight. In the days before September 11th no one could
have anticipated the horror that was about to unfold. What we know now is
that the German phone number is the key to the government’s case
connecting Moussaoui to the September 11th conspiracy. We’ll never know
what might have happened if the FBI had been able to make that connection
in the days before September 11th.

Osama bin Laden and his network of
terrorists are believed responsible for the Sept. 11, 2001,
attack on the Pentagon and World Trade Center as well as other
terrorist acts against America. Follow their shadowy path from
desert training camps to the epicenter of human
tragedy.